I currently have a Sta-rite PLD50 filter on my pool. Not sure how old it is but we’ve had it for 3 years and got from a friend. The cartridge needs to be replaced but I’ve seen $260-399 for it to be replaced. Should I replace it or switch to a different filter? There is no backwash and I’m currently trying to clear the pool and I’ve used 18 lbs of de and it’s still not clear.